Automatic controlling means for aircraft



l' G. N. HANSON ETAL 1 2,392,381

AUTOMATIC CONTROLLING MEANS FOR AIRCRAFT Filed May 15, 1942 s Sheeis-Sheet 1 INVENTORSZ GERALD N. HANSON ERCY HAL ARL A. FR

Jan. 8, 1946.

Filed May 15, 1942 3 Sheets-Sheet 2 TRIM TAB CONTROL INVENTOR T GERALD N. HANSON PERCY- HALPERT CARL A. RISCHE ATTORNEY.

Jan. 8', 1946. G. N. HANSON. ETAL 2,392,381

' AUTOMATIC CONTROLLING MEANS FOR AIRCRAFT Filed May 15, 1942 3 Sheets-Sheet a m MN 45 87 0 .wt g on Film MIL J INVENTORS: GERALD N. HANSON PERCY HALPERT .(ZARL A. FRISCHE CRNEY.

Patented Jan. 8, 1946 AUTOMATIC CONTROLLING MEANS FOR AIRCRAFT Gerald N. Hanson, Allendale, N. J., and Percy Halpert, Kew Gardens, and Carl A. Frische, Great Neck, N. Y., assignors to Sperry Gyroscope Company, Inc., Brooklyn, N. Y., a corporation of New York Application May 15, 1942, Serial No. 443,146

2 Claims.

This invention relate to control devices for aircraft. More particularly, the invention is concerned with automatic pilots for positioning an aircraft by means of its elevator, ailerons or rudder.

The primary feature of the present invention is a cable release by which the main cable drum of the automatic pilot may be positively freed from the servo motor by which it is normally driven.

Other objects, features and structural details of the invention will be apparent from the following description when read in connection with the accompanying drawings, wherein Fig. 1 show a schematic diagram illustrating, in exploded relation, the component parts of a servo motor control unit constructed in accordance with the present invention.

Fig. 2 is a schematic view and wiring diagram of the improved trim tab control of the automatic pilot.

Fig. 3 is a side elevation showing the general casing construction of the improved servo motor unit, the cable drum structure and the driving and releasing mechanism for the same being illustrated in vertical section.

Fig. 4 is a detail front elevation, slightly reduced in size, showing the cable drum and releasin mechanism.

Fig. 5 is a section view taken on line 55, in

Fig. 3, and

Fig. 6 is a detail perspective view illustrating th slot in the central connecting arm of the cable drum release mechanism.

With reference to the drawings and particularly Fig. 2', one of the control surfaces for aircraft, such as the elevator, is shown to include a main surface l pivoted at H in the tail of the craft and a trim tab or auxiliary surface H which is pivoted at It on the main surface. The elevator may be moved under control of either the automatic pilot as hereinafter more particularly described, or th human pilot by suitable connecting linkage (not shown). The trim tab is similarly controlled in an independent manner, the manual control for this surface,'being of a suitable and well known construction, not being illustrated in the drawings. A cable linkage M connects the main surface l0 so that movement is transmitted to the same from the cable drum l of the servo motor of the automatic pilot. In accordance with the teaching of the invention, the trim tab I2 is independently positioned by motive means consistin of a reversible motor, indicated at l5, whose movement is transmitted by way of drum I'I, cable l8, pulley l9 and linking cables 20 to the same, in a manner hereinafter more particularly described.

In Fig. 1, the servo unit of the automatic pilot is shown to include a controlling torque motor whose stator windings 2| are fed by an electrical signal from an elevator servo amplifier circuit of the character particularly described in the copending application of George P. Bentley and Carl A. Frische, Serial No. 259,178, filed March 1, 1939. The armature 22 of the controlling magnetic motor is mounted to rock about an axis 23 and position the rocker arm 24 and the respective valves 25 and 26 which are pivotally connected to the arm 24 at opposite ends of the same by means of the valve stems 21 and 28. The servo unit of the automatic pilot also includes, in the present instance, a three gear type hydraulic pump, indicated at 29, which is driven by a motor .30 that is energized from a suitable source of electrical energy, as indicated at 3|. As shown, pump 29 delivers oil or other fluid to the respective valves and 26 by way of pipes 32 and 33, the return flow of the fluid to which the valves offer but small resistance in their normal positions being made by Way of the common pipe 34, sump 35 and pump intake pipes 36 and 31. The outlet pipes of the pump 29 also communicate with the respective ends of the main servo 'cylinder 38 and auxiliary servo cylinder 39. Such connection is accomplished as shown in Fig. l by therespective pipes all and M In the present instance, auxiliary cylinder 39 is constructed of smaller size than the main cylinder 38. It will 'be understood that movement of pistons 33 results from a change in the normally balanced pressure in opposite sides of the main servo cylinder 38- and that such motion is also communidated to the pistons 42 of the auxiliary servo cylinder 39. Control ov r the servo unit is exercised by the torque motor whose coils or windings 2i are connected across the output-of an amplifier circuit which normally applies the same voltage across each coil. The magnetic armature 22 consequently is affected by equal and opposite torque and therefore exerts no force to tend to close either of the valves 25 or 26. When the signal for the torqu motor is unbalanced, the armature 22 is rocked and the valves 25 and 26 moved correspondingly which differentially restricts the free flow of fluid from the pump 29 through the valves and sump 35 back to the pump. The pump consequently builds up a pressure to overcome the restriction caused by unbalancing of the valves which results in the controlling movement of the pistons 43 and 42. Piston movement of the main When automatic flight control is not required,

teaching of the present invention such a result is obtained without using an additional oil by-pass by a means for centralizing the differential controlling valves 25 and 26 of the servo unit. As

shown in Fig. 1, means are provided in the form of a forked'arm 41 whose spread ends engage the undersurface of two spaced blocks 48 rigidly mounted on the rocker arm 24. Engagement of arm 41 with blocks 46 is effected by means of spring 49 which urges the parts into a position to centralize the rocker 24 and valves 25 and 26. The spring 4915 rendered normally ineffective by means of solenoid 50 which is situated in series in the circuit supplying the pump motor 30. The central stem of the forked arm 4| provides an armature for the solenoid 50 which is effective as long as energy is supplied to drive the pump motor to disable the spring 49 and permit the servo motor to respond to signals for automatic flight. When the circuit to the pump motor 39 is opened, the pump ceases functioning and the solenoid 50 is no longer energized, which restores the system to the control of the spring 49 which is then effective to centralize the rocker arm 24 with the valves 25 and 26 in their full open position, the effect of the spring overcoming in a positive manner the torque motor armature to which the arm 24 is directly connected. This permits the fluid to by-pass freely through the control valves as soon as the power to the pump drive motor is removed.

With reference to Fig. 2, the automatic trim regulator is shown controlled from the auxiliary servo cylinder 39. Movement of the connected pistons 42 is transferred to a contacting element which is adapted to move between two nor- I mally open switches 52 and 53 which have cooperating pieces forthe element 5|. Switches 52 and 53 may be of the snap, micro switch type'and are closed when the moving contact 5| engages either one of the respective cooperating pieces of the same. Independent circuits containing the include, in the present instance, limit switches 54 and 55 which are. of the slide contact type. As shown, the normally closed switch 55 is in series with the switch 53 and switch 54 is likewise situated in a separate circuit which includes switch 52. The slide pieces of the respective norswitches 54 and 55 which operate to open either of the desired controlling circuits when the designed limits of travel of the surface are exceeded. A relay indicated'at H which is controlled by the individual switch including circuits described is included in a. normally open circuit for controlling the direction of operation of the reversible motor I6. The motor circuit is separately energized, in the present instance, by a suitable. source 62. Also, v the relay 6| includes,

as shown, a double pole switch 63 which is operated under control of solenoid coils 64 or 65 provided in the respective switch including circuits hereinbeforedescribed. It will be now understood that motor l6 will rotate in one direction upon closure of switch 53 by contact 5| and will rotate in the opposite direction when switch 52 has been closed. Such movement may continue as long as the controlling circuits remain closed. As shown, the movement of motor I 6 is respective normally open switches 52 and 53 also transferred to the drum I I by way of shaft 66 through a slip clutch connection indicated at 61, a releasable clutchconnection 68. and shaft 69. The speed of trim tab controlling motor I6 is adjusted so ,the movement of trim tab I2 is slow when compared relatively with motion of the main control surface I0 effected by means of the primary servo motor pistons 43. Hence the trim tab does not interfere with the main servo motor response and essentially integrates the pressure variations occurring in the cylinder of the same. A solenoid controlled toggle mechanism may be employed, as shown, to effect engagement of the clutch connection 68 when automatic trim tab control is desired. A switch 10 operable by the pilot may be employed in a separate solenoid including circuit for engaging or disengaging the clutch 68. It will be understood that as long as clutch 68 is disengaged, no movement of motor I6 will be transmitted to control drum I! so that the automatic trim tab control is ineffective while the automatic pilot is functioning normally. Also, in such event, control over the trim tab surface I2 is then capable of being manually effected by the human pilot.

With reference to the detail views, Figs. 4 to 6, inclusive, the casing of the main servo unit is indicated at H. The pinion-driven shaft 46 is rotatably mounted by means of the spaced roller bearings I2 in the casing II. Shaft 46 projects from the casing and cable drum I5 which is normally secured thereto transmits the movement of the rack 44 of the primary servo motor to the main control surface III of the aircraft. In accordance-with the teaching of the present invention, an emergency release device is provided for freeing the drum I5 from its driving shaft 46 in order to disable the automatic pilot when required. The structural arrangements employed for this purpose include a sleeve I3 which is fixed in position on the shaft. The cable drum I5 is, in this instance, freely mounted on the sleeve 13 which may be considered as part of the driving shaft 46. Two oppositely disposed, radially extending arms 14 and 15 are situated on the projecting end of the sleeve 13. The respective ends of the arms I4 and I5 are grooved radially to slidably receive dogs 16 and 11. Two mating slots 1.8 and 19 are provided in the periphery of the drum I5 to receive thedogs 16 and I1. When so received or engaged, dogs "I6 and 11 provide a means for locking the drum and shaft in motion communicating relation. Means for releasing the locking dogs is provided by two pairs of spring links as indicated at and 8 I. Links 80 are pivotally connected to dog 16 and to a slide block 82 while links 8| similarly join the dog 11 to the block. Block 82 is further positioned for movement axially of the shaft 46 and such movement is imparted to the samein one direction by means of a keyed rod 83 which fits in a central splined bore 84 in the shaft .46. Rod 93 can be urged I .cable 85 is consequently positioned to be twist free within the rotatably movable shaft 46. Cable 88 extends through a rotatably mounted bellshaped piece 81 situated in spaced axial relation to the shaft 48 on forwardly projecting portions of the sleeve 18. The cable 85 may be actuated by the human pilot through any suitable'connection (not shown) in order to release the drum l8. from shaft 88 to. disable the automatic pilot under emergency conditions. The lengths of the pairs of spring links are so designed that a force is applied by the same to keep the dogs 16 and "gin normal locking position between the parts when the block is pressed inwardly through dead center to a stop position in which the, block engages the end of shaft 48 as shown in Fig. 3. Springs 80 and 8| consequently form a toggle connection which normally tends to maintain the dogs in a locked position. A solid link 88 and 89 which is slotted at one end as indicated at 90, in

Fig. 6, is situated between the respective pairs of spring links so that a positive movement'of the toggle connection is obtained when the pivot pin is brought into engagement with either end of the slot. When the cable 85 is pulled by the pilot or otherwise actuated, the block 82 is forced to move in the direction of the arrow by the rod 83.

The springiinks of the toggle connection com-v press until a dead center position is reached after In the improved servo unit, the differential pistons 88 which move axially within the cylinder 88 are also capable of transverse adjustment with relation to the cylinder. As shown in Fig. 5, cup- L shaped leather piston forming members, as indicated at 8|, are fixed to the smaller, diameter metal pistons 48 which are connected by the rack 44. With this construction the piston element is pinion I! which meshes with rack 44 is transversely centered with relation to the servo cylinder. The roller bearing 92, in this instance, is similarly centered and contacts the smooth surface 93 of the rack opposite to the toothed surface of the same. The bearing 92 centers the pistons in transverse relation in the cylinder by setting arotatable member 94 which includes an eccentric portion 95 on which the provided roller bearing 92 rotates. The eccentrically positioned bearing 92 and member 94 consequently provide a means for adjusting the differential piston in demovable transversely of the cylinder and the an occurrence, the pitch line of rack II and the center of pressure of the pinion 45 are made coincident by means of an adjustable bearing 82 which is approximately placed on the same center line as the pinion in a position to take the downward thrust of the same due to loading. The

sired transverse relation within the cylinder.

As many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Having described our invention, what we claim and desire to secure by Letters Patent is:

1. In automatic pilots for aircraft having a control surface, a primary servo motor, a cable connection linking the surface and servo motor, a driving shaft controlled by the servo motor, a sleeve fixed to the shaft having radially extending arms, a cable drum freely mounted on said sleeve, a radially slidable dog engaged in contiguously positioned slots in said arms and said drum for normally locking said drum and shaft in motion communicating relation, yielding means for normally maintaining said dog in a locking position, and means for releasing said yielding means and sliding said dog from a locking position to free the drum from motion communicating relation to the driving shaft.

2. In automatic pilots for aircraft having a control surface, a primary servo motor, a cable connection linking the surface and servo motor, a driving shaft controlled by the servo motor, a sleeve fixed to the shaft having radially extending arms, a cable drum freely mounted on said sleeve, a radially slidable dog engaged in contiguously positioned slots in said armsand said drum for normally locking said drum and shaft- 

